Fix #2292: Do not crash when a top-level class is untyped

This can happen when the class is in a package that got an error type.

Author: smarter

compiler/src/dotty/tools/dotc/typer/FrontEnd.scala

@@ -70,7 +70,7 @@ class FrontEnd extends Phase {
   private def firstTopLevelDef(trees: List[tpd.Tree])(implicit ctx: Context): Symbol = trees match {
     case PackageDef(_, defs) :: _    => firstTopLevelDef(defs)
     case Import(_, _) :: defs        => firstTopLevelDef(defs)
-    case (tree @ TypeDef(_, _)) :: _ => tree.symbol
+    case (tree @ TypeDef(_, _)) :: _ => if (tree.hasType) tree.symbol else NoSymbol
     case _ => NoSymbol
   }
 

tests/neg/i2292.scala

@@ -0,0 +1,3 @@
+package + // error
+
+class Foo